Some prior studies had suggested that vitamin D might benefit these patients.

"Vitamin D is a very hot topic in medicine and many people in the United States have low vitamin D levels," noted one expert not connected to the study, Dr. Diane Horowitz, a rheumatologist at North Shore-LIJ Health System in Great Neck, N.Y.

"Vitamin D deficiency and insufficiency have been associated with a variety of medical conditions," Horowitz said. "There is conflicting evidence of the role of vitamin D supplementation in alleviating the signs and symptoms of osteoarthritis."

The new two-year study included nearly 150 patients with an average age of 62 who had knee osteoarthritis and took either an inactive placebo or 2,000 international units per day of a form of vitamin D called cholecalciferol.

By the end of the study, patients who took the vitamin D supplements had no significant differences in knee pain or cartilage loss compared to those who took the placebo, according to a team led by Timothy McAlindon, of Tufts Medical Center in Boston, and colleagues.

Knee osteoarthritis is a common age-related disease that has a significant effect on patient mobility and, therefore, society, in terms of missed work, early retirement and surgical treatment, the study authors said in the report, which was published in the Jan. 9 issue of the Journal of the American Medical Association.

"Despite its impact, there are no medical treatments established to influence the course" of knee osteoarthritis, McAlindon's team noted in the study.

Horowitz said that although the study showed no effect for vitamin D against knee osteoarthritis, maintaining a proper level of the nutrient is essential to good health. That means "people who are found to be deficient in vitamin D should follow their doctor's advice and replete their vitamin D," she said.